Sunan an-Nasa'i, Volume 2, Book 18, Hadith 1536 (DarusSalam) ⓘ

It was narrated that Ibn 'Abbas said: "The fear prayer was no more than two prostrations like the prayer of these guards of yours today behind the Imams of yours, except that it was one group after another. One group stood, although they were all behind the Messenger of Allah, and one group prostrated with him, then the Messenger of Allah stood up and they all stood with him. Then he bowed and they all bowed with him, then he prostrated and those who had been standing the first time prostrated with him. When the Messenger of Allah and those who had prostrated with him at the end of their prayer sat, those who had been standing prostrated by themselves, then they sat and the Messenger of Allah said the taslim with all of them.

أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ سَعْدِ بْنِ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا عَمِّي، قَالَ حَدَّثَنَا أَبِي، عَنِ ابْنِ إِسْحَاقَ، قَالَ حَدَّثَنِي دَاوُدُ بْنُ الْحُصَيْنِ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ مَا كَانَتْ صَلاَةُ الْخَوْفِ إِلاَّ سَجْدَتَيْنِ كَصَلاَةِ أَحْرَاسِكُمْ هَؤُلاَءِ الْيَوْمَ خَلْفَ أَئِمَّتِكُمْ هَؤُلاَءِ إِلاَّ أَنَّهَا كَانَتْ عُقَبًا قَامَتْ طَائِفَةٌ مِنْهُمْ وَهُمْ جَمِيعًا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَسَجَدَتْ مَعَهُ طَائِفَةٌ مِنْهُمْ ثُمَّ قَامَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَقَامُوا مَعَهُ جَمِيعًا ثُمَّ رَكَعَ وَرَكَعُوا مَعَهُ جَمِيعًا ثُمَّ سَجَدَ فَسَجَدَ مَعَهُ الَّذِينَ كَانُوا قِيَامًا أَوَّلَ مَرَّةٍ فَلَمَّا جَلَسَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَالَّذِينَ سَجَدُوا مَعَهُ فِي آخِرِ صَلاَتِهِمْ سَجَدَ الَّذِينَ كَانُوا قِيَامًا لأَنْفُسِهِمْ ثُمَّ جَلَسُوا فَجَمَعَهُمْ رَسُولُ اللَّهِ صلى الله عليه وسلم بِالتَّسْلِيمِ ‏.‏